[whswhs]

The rule of 16 makes sense to me, in that anyone, no matter how skilled, may once in a while fail at performing a task. If you want to have any failures at all, an 18 has to fail; if you want to distinguish ordinary and catastrophic failure, an 18 needs to be catastrophic and a 17 ordinary. The odds actually give you far more failures than are realistic; I tend to think of them as "this is the time when the heroes are on camera, and interesting things will tend to happen," and to assume that the time when they're not being roleplayed is time when everything is going smoothly.

If you had a story where the heroes always succeeded at their main skills, and were defeated only by hopeless odds, that wouldn't make a very interesting narrative or drama, I think.

As for the rule of 20, if you look at defaults, a character with attribute 20 defaults to 16 for Easy skills, 15 for Average, and 14 for Hard. All of these are greater than ordinary professional competence. You're not quite looking at Clark Savage, Jr. or Bruce Wayne, but you're not far short. That's already pushing at the limits of believability. If it were up to me, the rule of 20 would change to rule of 16, with defaults of 12, 11, or 10—still pretty good, but not "trained professional" as default. But imagine letting it go higher—IQ 22 would make you the equally of a highly skilled professional at Artist, Diplomacy, Engineer (all specializations!), and Physician, among others. The limit helps lessen the strain on the players' disbelief suspension.

I don't think these narrative concerns are the same as "game balance."